Benefic/Benefic II potency is not the major problem with AST, otherwise Noct would be a whole lot better than people give it credit for. WHM/SCH usually overheal with 400 potency anyways when combined with each other's heals.
The problems are chiefly:
1. Astrologian suffers from a lack of emergency heals. They have Essential Dignity, end of list, unless you're really stretching and counting Benefic II procs. WHM/SCH have much more reliable and powerful ways to bring people back from low HP.
2. Nocturnal Stance is miles behind Scholar due to lack of fairy, lack of utility outside of cards, lack of powerful shielding options (Adlo vs. Aspected Benefic), lack of MP management, lack of safe ability to DPS, and lack of useful skills (Collective Unconscious....blech)
3. Diurnal Stance is comparable to White Mage but still severely weaker due to lack of healing thoroughput. Astrologian has more utility compared to WHM in exchange for the lack of MP management and ability to buff healing thoroughput.
4. Points 2 and 3 mean that Nocturnal Stance is comparatively useless.
5. A lot of their oGCD skills are very limited in use. Collective Unconscious is almost always a worse option than just healing people unless you're in danger of running out of mana; Celestial Opposition's best use is using it on yourself to get 1 or 2 more ticks out of Luminiferous Aether. Disable is pretty awful when compared to Virus/Eye for an Eye. Royal Road is only a good option if you get Spire/Ewer and don't need either and Shuffle isn't up. Lightspeed is useless in most current fights because of the potency hit except for when you need an instant Stoneskin for whatever reason.
6. Card buffs are currently too weak to make up for any of these shortcomings.
My suggestions are as follows:
Aspected Benefic: Nocturnal Stance: Cure potency of 200 [210] with a shield of 150 [157.5] potency + 5% of target's maximum health.
Enhanced Benefic II: Instead of instant cast Diurnal Sect: Adds 12s to Aspected Benefic Regen Timer [+300 Potency total] Nocturnal Sect: Additionally restores 10% of the target's Maximum HP. Still has a 15% proc rate.
Lightspeed: Next 2 spells have no cast time and do not incur the global cooldown, but cost 25% more mana. 120s Recast.
Disable: Reduces target's damage by 10% for the next 10 seconds. 60s Recast.
Collective Unconscious: Diurnal Sect: Gives 20% Haste to all allies within range while channeled Nocturnal Sect: Increases potencies on all allies' skills by 10% while channeled Both Sects: 120s Recast, maximum 10s channel. Extends duration of all buffs placed by the caster while channeled. Shares a recast timer with Celestial Opposition.
Celestial Opposition: Stuns all enemies for 10s and restores 10% of self's mana. Doubles effect of cards on all targets 120s Recast. Shares a recast timer with Collective Unconscious.
Shuffle: Can't draw the same card, 60s Recast.
Royal Road: Burns current card to instantly draw a new card with an additional effect, but cannot draw the same card. 90s Recast. Enhanced Royal Road: Doubles effect of next card used | Expanded Royal Road: Spreads card to all nearby party members with 30% reduced effectiveness | Extended Royal Road: Doubles duration of next card used.
Spread: Can be used out of combat. 30s Recast after card is used.
Spear: Additionally reduces spells currently on recast timer by same amount of their maximum recast.
Spire/Ewer: Refresh/TP Equivalent over next 21s.
This way they have basic healing capabilities with a high-mana cost Emergency heal through Lightspeed.
The Nocturnal Stance aspected benefic is now actually useful on tanks but still not as strong as a critted Adlo from SCH (it's about half of a SCH's normal Adlo shield + 650-1000 HP depending on how much the target has -- can be adjusted if too strong/too weak without making it an exact copy of SCH shield and makes Lightspeed Stoneskin a very good way to mitigate damage).
Disable is just better now.
Enhanced Benefic II adds something unique to each Sect but 10% might be a little too high for the Nocturnal Sect (it's 2000 extra healing on a 20k HP target). I don't know how much healers heal for at level 60 in i190 gear though so I had no frame of reference.
Collective Unconscious and Celestial Opposition both now have additional effects that support their cards similarly to RR except you can more easily choose when to use it, while Collective Unconscious gives the party a similar buff to what their chosen Sect gives them while it's channeled. Celestial Opposition also has MP Management attached to it, which makes the trade-off between the two abilities situational in addition to how they affect cards.
Royal Road now draws you a card instantly that you can Shuffle to get a different card to use the buff on (which has a shorter recast) or use Spread on (also has a shorter recast). This makes cards MUCH more reliable.
Spire and Ewer now regenerate MP/TP over 21s instead of reduce costs, which makes them more useful throughout the fight.
The card effects themselves aren't buffed, but AST now has better ways to mitigate RNG and can use their other skills to additionally empower the cards, making them a very complex class.
Of course, not all of these changes need to be implemented because AST would likely be WAY overpowered with all of these. Potencies need to be tweaked if these buffs were passed. I doubt SE has anything as drastic as these changes planned, though....it's nice to fantasize.